Remove `disableMarkdown` setting
Remove `disableMarkdown` setting

This was used by the old composer to control whether to interpret text as markdown prior to sending.

The new setting is `MessageComposerInput.isRichTextEnabled`.

matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk,aperezdc/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk,aperezdc/matrix-react-sdk